It is in Chapter 8 that we are first introduced to Fagin, as Oliver enters the lair of the criminals. In a sense, Dickens has created a caricature of the criminal Jew in Fagin. Note how he is first described:
In a frying pan, which was one the fire and which was secured to the mantel shelf by a string, some sausages were cooking, and standing over them, with a toasting fork in his hand, was a very old shrivelled Jew, whose villainous looking and repulsive face was obscured by a quantity of matted red hair. He was dressed in a greasy flannel gown, with his throat bare, and seemed to be dividing his attention between the frying pan and a clotheshorse, over which a great number of silk handkerchiefs were hanging.
Note the way this first introduction emphasises the comparison between Fagin and the Devil - he is holding a toasting fork and standing next to the fire, and has "matted red hair."
Fagin in the novel then is clearly a master criminal, having set up a gang of child thieves and operating as their head, taking what they gain. It is clear in the novel that he is depicted as a character that has no loyalty except to himself. He exploits and manipulates others to suit his purposes, turning on Bill Sikes as it suits him and even going as far as trying to get Nancy to kill him. When he is eventually caught and sentenced to death, we are told that he goes mad when he realises that nobody at all cares about him and he will die giving pleasure to the audience who will watch him being hanged. He dies, alone and unloved, which we are meant to see as justice for his evil crimes throughout the novel and his deliberate plotting of Oliver's hanging.